The present invention relates to a crane control of a crane which includes at least one cable for lifting a load. Furthermore, the present invention relates to a further configuration of the crane control of a crane which includes at least one first and one second strand of cables for lifting a load. The crane control drives the positioners of the crane. In particular, the crane is a boom crane which has a boom to be swivelled about a horizontal axis, which is hinged to a tower rotatable about a vertical axis. For this purpose, a luffing gear and a slewing gear are provided as positioners. The cable for lifting the load runs over the tip of the boom, in particular over one or more deflection pulleys arranged there, so that the load can be moved in tangential direction by slewing the tower and in radial direction by luffing up the boom. In the embodiment of the invention with at least one first and one second strand of cables, both strands of cables extend from the tip of the boom to a suspension element such as a hook. The length of the cable can be adjusted by a corresponding drive, in order to move the load in vertical direction. In particular, the crane control of the invention generally relates to rotary cranes as well as mobile harbour cranes, ship cranes, off-shore cranes, truck cranes and crawler cranes.
From DE 100 64 182 and DE 103 24 692, whose entire contents form part of the present application, crane controls are known, whose control and automation concepts prevent the pendular movement of the load on the cable during a movement of the crane.
From DE 100 29 579 and DE 10 2006 033 277, whose contents likewise form part of the present application, there are furthermore known crane controls which prevent a rotary oscillation of the load on the cable.
In the above-mentioned crane controls, gyroscope units are used for determining the load oscillation, which are arranged in the hook of the crane and determine the angular velocity of the cable. The cable angle is determined via an observer circuit which integrates the movement of the cable. To be able to compensate the resulting offset, a freely swinging pendulum is assumed, whose rest position corresponds to a perpendicular cable angle. Such procedure is quite useful for damping the cable oscillation, as for this purpose the movements of the cable must be monitored above all when the load is swinging freely on the cable. However, a determination of the absolute alignment of the cable, in particular before the load can swing freely, neither is provided nor possible in the known crane controls. Furthermore, known sensor arrangements and crane controls have had the disadvantage that disturbing influences such as the cable field twisting were not taken into consideration in the load oscillation damping for damping the spherical pendular oscillations of the load.
Known systems, however, as they are used e.g. in cranes with a trolley merely movable in horizontal direction, and which employ measurement camera systems for determining the absolute cable angle, cannot be used in particular in boom cranes. Measurement camera systems always must be arranged directly behind the cable checkpoint, in order to be able to determine the cable angle. In the case of boom cranes, however, in which the cable is movably guided over a deflection pulley arranged at the boom head, no cable checkpoint does exist, as the cable exit point likewise changes with the cable angle. Measurement pick-ups, which mechanically determine the cable angle relative to the boom, are just as useless for measuring the absolute cable angle, as they operate inaccurately, first of all, and in addition lead to wrong results in the case of a deformation of the crane. Moreover, all these systems always only determine the cable angle relative to the boom, and thus would only indirectly be useful for determining the absolute cable angle, so that such solutions so far have completely been omitted.
Before hoisting or at the beginning of hoisting, the crane operator therefore must still align the crane manually and at sight, such that the cable is aligned substantially perpendicular. Especially with the great distance from the load, however, this is often possible only with great difficulty, so that deviations of the cable angle from the plumb line are obtained, which lead to undesired oscillations when lifting the load. The same problems arise when due to an imbalance of the load the cable is aligned perpendicularly before hoisting, but when lifting the load the cable angle is changed by the movement of the center of gravity of the load below the load suspension point. The yielding of the crane structure under the load when lifting the load also can change the cable angle unintentionally. Off-shore cranes additionally involve the problem that the cable angle can be changed by a relative movement of a ship carrying the load with respect to the off-shore crane.